Problems have existed in the past when using fasteners to fasten panels made from composite materials, such as graphite composite and other soft materials. Typical problems have included damage to the panels resulting from installation forces required to properly install the fastener. For example, when very thin or soft sheets of material are utilized in the inner panel, the force applied by the fastener against the inner panel when the fastener is being set often deforms and sometimes crushes the inner panel and thereby weakens it at that point. As a result, the fastener never reaches a fully set condition. When this occurs, the panel often must be discarded and replaced, and significant time and money usually are lost.
Fasteners have been developed to overcome the above problems of fastening panels made of composite materials. One such fastener is disclosed in the inventor's U.S. Pat. No. 4,457,652 and comprises a fastener body inserted in aligned openings in the panels, and a drive stem threadedly mounted through the fastener body. Turning motion of the stem relative to the fastener body moves the stem axially outwardly through the fastener body and deforms a sleeve into overlying contact against the inner panel. The sleeve is provided with a thin walled section adapted to deform laterally and produce a sufficient blind side bearing surface against the inner panel without damaging it.
Other types of fasteners have been developed to fasten panels of composite materials without damaging them, such as conventional rivets with washers, multiple-piece bolts and rivets, bi-metallic rivets, and other types of fasteners. However, such fasteners and rivets generally are relatively expensive to manufacture and are not of a one-piece integral construction so that relatively significant amounts of time are needed to install them, or they do not form a satisfactory upset against the composite material.
Accordingly, there has existed a definite need for another type of fastener for joining panels of composite materials that produces a large bearing surface without damage to the inner panels, and which is a one-piece, low cost assembly for simple and quick installation using conventional setting tools. The present invention satisfies this need and provides further relate advantages.